NaN is mostly equivalent to the _mathematical_ concept of undefined. It cannot be equal to anything, even itself, because there are multiple mathematical operat

NaN is mostly equivalent to the _mathematical_ concept of undefined. It cannot be equal to anything, even itself, because there are multiple mathematical operations that can result in NaN that are not equivalent in value. Considering their result equivalent would be in error. in a NaN === NaN world, (1/0)*0 === 0/0 is true.